Spawning prefab on touch after previous spawn(s) had been destroyed

Question

I wrote a script which pawns an object (instantiated prefab) each time the player touches the screen.

The maximum number of these spawned objects active in the scene at once is 3, and when they are not visible they will be destroyed. I need these prefabs to be able spawn again after they had been destroyed.

I tried this but it does not work...

This script is added to a game object called "canCreator" in my scene hierarchy:

public class CreatingCan: MonoBehaviour 
{
    public GameObject Can;
    public int numberOfCans;
    public bool canSpawn = true;

    private void Start()
    {      
        numberOfCans = 0;
    }
    void Update()
    {
        if (Input.touchCount > 0)
        {          
            Touch touch = Input.GetTouch(0);
            Vector2 TouchPosition = Camera.main.ScreenToWorldPoint(touch.position);
            if (touch.phase == TouchPhase.Began && canSpawn == true)
            {      
                if (Instantiate(Can, TouchPosition, Quaternion.identity))   
                {
                    numberOfCans++;                
                }
            }
        }
   
        if (numberOfCans >= 3)
        {
            canSpawn = false;
        }

    }

}

This script is on my can prefab:

public class fallingCan : MonoBehaviour 
{
    CreatingCan CC;
    private void Update()
    {
       
        if (transform.position.x < Camera.main.transform.position.x - 10)
        {
            Destroy(gameObject);
               CC.numberOfCans--;     
        }    
    }
}

Answer 1

A simple trick I like to use is introduce a self-counting object script:

public class CountedObject : MonoBehaviour {

    static int _count;

    void OnEnable() { _count++; }

    void OnDisable() { _count--; }

    public int GetActiveCount() { return _count; }
}

Then your spawner can look like...

public class CreatingCan: MonoBehaviour 
{
    public CountedObject canPrefab;
    public int spawnLimit = 3;
    public bool canSpawn = true;

    void Update()
    {
        // Don't spawn more if we've disabled spawning, or are at/above our limit.
        if (!canSpawn || canPrefab.GetActiveCount() >= spawnLimit)
            return;

        // Check all touches, not just the first one, so it works even if you
        // hold one finger on the screen, and tap with another.
        for (int i = 0; i < Input.touchCount; i++) {
            var touch = Input.GetTouch(i);
            if (touch.phase != TouchPhase.Began)
                continue; // Skip any old touches.

            Vector2 touchPosition = Camera.main.ScreenToWorldPoint(touch.position);
            Instantiate(canPrefab, touchPosition, Quaternion.identity)

            // Abort if we hit our limit, even if there are still more touches.
            if (canPrefab.GetActiveCount() >= spawnLimit)
                break;
        }
    }    
}

Answer 2

Here's your problem:

if (numberOfCans >= 3)
{
    canSpawn = false;
}

You never set canSpawn to true after this.

Maybe what you wanted is canSpawn = (numberOfCans >= 3). This will update canSpawn each frame.